Recently, in the field of mechanical element for optical disk drives such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD-RAM, DVD-RW, DVD+RW and MD intended to use in personal computers, audios, game players and the like, move to resinification is proceeding for the purpose of reducing the weight and cost and improving the productivity. In particular, resinification by a filler-reinforced polyphenylene ether or polycarbonate resin is actually performed in many cases mainly for optical pickup and chassis such as pickup chassis, sub-chassis and base chassis.
However, to cope with recent progress to higher performance of optical disk drives, such as reduction in thickness, the mechanical element for optical disk drives is demanded to ensure the strength, rigidity, dimensional precision and moldability while satisfying higher heat resistance and smaller thickness. Also, in the case of an optical disk drive such as CD player, DVD player and DVD navigation mounted on a car subject to a severe use environment in view of temperature, vibration or the like, resinification is not proceeding due to problems in reliability, durability and the like.
Polyphenylene ether resins or polycarbonate resins cannot satisfy those characteristics required of the mechanical element for optical disk drives particularly in view of heat resistance and mold flowability. Also, studies are being made on resinification with a super engineering plastic such as polyphenylene sulfide resin and liquid crystal polymer, however, despite excellent performance in view of heat resistance, these resins have a problem in the dimensional precision, moldability (e.g., bur), weld strength, increase in the weight, cost and the like and their application to a mechanical element for optical disk drives is difficult in many cases.
Under these circumstances, a resin composition comprising not a single resin but two or more resins is used with an attempt to solve those problems. For example, Patent Documents 1, 2 and 3 have proposed a resin composition comprising a polyphenylene sulfide resin and a polyphenylene ether resin or the like.
However, in Patent Documents 1 and 2, the compatibilizing agent for effectively mixing two different resins and the inorganic filler for improving the heat resistance, mechanical strength, dimensional precision and the like are not satisfactorily designed and various effects required of the mechanical element for optical disk drives are not satisfied. For example, in Patent Document 1, the dimensional precision decreases (the deviation of the optical axis become marked) if the ratio of resin component is large, and therefore, the resin component is specified to be from 30 to 56 vol %. This corresponds to less than 40 wt % of the resin component. In general, if the ratio of resin component is reduced, a problem is sometimes generated in the flowability to adversely affect the moldability. In Patent Document 2, glass fiber and calcium carbonate are used in combination for the purpose of satisfying both the dimensional precision and the mechanical strength, however, the content of the resin components is small also in the Examples of this patent application and the same problem as above is caused.
In Patent Document 3, the compatibilizing agent and inorganic filler are studied, but the resin composition is intended to use for secondary battery case and has a problem in that various characteristics required of the mechanical element for optical disk drives are not fully satisfied.
In this way, a thermoplastic resin capable of satisfactorily coping with the resinification of mechanical element for optical disk drives having high performance or used in a severe environment, for example, mounted in a car, is not known at present and it is keenly demanded to develop a resin-made mechanical element constituted by a resin material satisfying all of heat resistance, mechanical strength, dimensional precision, moldability, low specific gravity, mold releasability (releasability from mold) and flame retardancy.
Patent Document 1: JP-A-2001-294751 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)
Patent Document 2: JP-A-2002-69298
Patent Document 3: JP-A-2002-12764